LED fluorescent lamp

ABSTRACT

A light-emitting diode (LED) fluorescent lamp which can replace a typical fluorescent lamp is provided. The LED fluorescent lamp includes an LED array including a plurality of LEDs connected in series; first through fourth connection pins; first through fourth capacitors connected to the first through fourth connection pins, respectively; a first diode having an commonly connected to second ends of the first and third capacitors and a cathode connected to a first end of the LED array; a second diode having an anode connected to a second end of the LED array and a cathode commonly connected to second ends of the second and fourth capacitors. The LED fluorescent lamp can replace a typical fluorescent lamp without a requirement of the installation of additional equipment or the change of wiring.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application Nos.10-2008-101413 filed on Oct. 16, 2008, 10-2008-109048 filed on Nov. 4,2008, 10-2008-123444 filed on Dec. 5, 2008, and 10-2009-0018268 filed onMar. 4, 2009 in the Korean Intellectual Property Office, the disclosureof which are incorporated herein by reference in their entirety. Thisapplication is also continuation of application Ser. No. 13/708,267filed on Dec. 7, 2012 which is a continuation of application Ser. No.12/473,098 filed on May 27, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting diode (LED)fluorescent lamp, and more particularly, to an LED fluorescent lampwhich is suitable for use, instead of a typical fluorescent lamp, with afluorescent lamp ballast.

2. Description of the Related Art

Due to the improvement of the optical efficiency of light-emittingdiodes (LEDs), which are previously used as low-power indicator lights,the range of application of LEDs has gradually widened. LEDs, unlikeother light sources, do not contain mercury and are thus deemed asenvironment-friendly light sources. Therefore, LEDs have recently comeinto the limelight as next-generation light sources for mobileterminals, liquid crystal display (LCD) TVs, or automobiles.Accordingly, incandescent lamps or fluorescent lamps, which have beenused as major light sources for the past hundred years, are rapidlybeing replaced by LEDs.

LED lamps can directly replace incandescent lamps such as E26 baselamps. However, in order to replace existing fluorescent lamps with LEDlamps, it is necessary to change lamp fixtures or to additionallyinstall a power supply exclusive for LED lamps. Thus LED fluorescentlamps have not yet been widely distributed.

SUMMARY OF THE INVENTION

The present invention provides a light-emitting diode (LED) fluorescentlamp which is suitable for use, instead of a typical fluorescent lamp,in an existing fluorescent lamp fixture without a requirement of theinstallation of an additional fluorescent lamp ballast exclusively forthe LED fluorescent lamp or the modification of internal wiring of thefixture.

According to an aspect of the present invention, there is provided anLED fluorescent lamp including a plurality of external connection pins;an LED array including a plurality of LEDs connected in series; and oneor more capacitors connected between the LED array and the externalconnection pins and varying the impedance of an electronic fluorescentlamp ballast connected to the LED fluorescent lamp through the externalconnection pins.

According to another aspect of the present invention, there is providedan LED fluorescent lamp including an LED array including a plurality ofLEDs connected in series; first through fourth connection pins; a firstcapacitor connected between the first connection pin and a first end ofthe LED array; a second capacitor connected between the secondconnection pin and a second end of the LED array; a third capacitorconnected between the third connection pin and the first end of the LEDarray; and a fourth capacitor connected between the fourth connectionpin and the second end of the LED array.

According to another aspect of the present invention, there is providedan LED fluorescent lamp including an LED array including a plurality ofLEDs connected in series; first and second connection pins; a firstcapacitor having a first end connected to the first connection pin and asecond end connected to a first end of the LED array; a second capacitorhaving a first end connected to the second connection pin and a secondend connected to a second end of the LED array; and one or more diodesconnected between the first and second connection pins and generating aunidirectional current path in the LED array.

According to another aspect of the present invention, there is providedan LED fluorescent lamp including an LED array including a plurality ofLEDs connected in series; first through fourth connection pins; firstthrough fourth capacitors connected to the first through fourthconnection pins, respectively; a first diode having an anode commonlyconnected to second ends of the first and third capacitors and a cathodeconnected to a first end of the LED array; a second diode having ananode connected to a second end of the LED array and a cathode commonlyconnected to second ends of the second and fourth capacitors; a thirddiode having an anode connected to the cathode of the second diode and acathode connected to the first end of the LED array; and a fourth diodehaving an anode connected to the second end of the LED array and acathode connected to the anode of the first diode.

According to another aspect of the present invention, there is providedan LED fluorescent lamp including an LED array including a plurality ofLEDs connected in series; first through fourth connection pins; firstthrough fourth capacitors connected to the first through fourthconnection pins, respectively; a first diode having a cathode connectedto a first end of the LED array; a second diode having an anodeconnected to a second end of the LED array; a third diode having ananode connected to a second end of the first capacitor and a cathodeconnected to the anode of the first diode; a fourth diode having ananode connected to the cathode of the second diode and a cathodeconnected to a second end of the second capacitor; a fifth diode havingan anode connected to a second end of the third capacitor and a cathodeconnected to the anode of the first diode; a sixth diode having an anodeconnected to the cathode of the second diode and a cathode connected toa second end of the fourth capacitor; a seventh diode having an anodeconnected to the second end of the LED array and a cathode connected tothe second end of the first capacitor; and an eighth diode having ananode connected to the second end of the second capacitor and a cathodeconnected to the first end of the LED array.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail preferred embodimentsthereof with reference to the attached drawings in which:

FIG. 1 illustrates a circuit diagram of a light-emitting diode (LED)fluorescent lamp according to a first exemplary embodiment of thepresent invention;

FIG. 2 illustrates a circuit diagram of an LED array shown in FIG. 1;

FIG. 3 illustrates a circuit diagram of an LED fluorescent lampaccording to a second exemplary embodiment of the present invention;

FIG. 4 illustrates a circuit diagram of an LED fluorescent lampaccording to a third exemplary embodiment of the present invention;

FIG. 5 illustrates a circuit diagram of an LED fluorescent lampaccording to a fourth exemplary embodiment of the present invention;

FIG. 6 illustrates a circuit diagram of an LED fluorescent lampaccording to a fifth exemplary embodiment of the present invention;

FIG. 7 illustrates a circuit diagram of an LED fluorescent lampaccording to a sixth exemplary embodiment of the present invention;

FIG. 8 illustrates a circuit diagram of an LED fluorescent lampaccording to a seventh exemplary embodiment of the present invention;

FIG. 9 illustrates a circuit diagram of an LED fluorescent lampaccording to an eighth exemplary embodiment of the present invention;

FIG. 10 illustrates a circuit diagram of an LED fluorescent lampaccording to a ninth exemplary embodiment of the present invention;

FIG. 11 illustrates a circuit diagram of an LED fluorescent lampaccording to a tenth exemplary embodiment of the present invention;

FIG. 12 illustrates a circuit diagram of a half-bridge-type electronicfluorescent lamp ballast to which the LED fluorescent lamp of the fourthexemplary embodiment is applied;

FIG. 13 illustrates a circuit diagram of an instant start-typeelectronic fluorescent lamp ballast to which the LED fluorescent lamp ofthe fourth exemplary embodiment is applied;

FIG. 14 illustrates a circuit diagram of an instant start-typeelectronic fluorescent lamp ballast to which the LED fluorescent lamp ofthe sixth exemplary embodiment is applied;

FIG. 15 illustrates a circuit diagram of an instant start-typeelectronic fluorescent lamp to which the LED fluorescent lamp of theseventh exemplary embodiment is applied;

FIG. 16 illustrates a circuit diagram of an instant start-typeelectronic fluorescent lamp ballast to which the LED fluorescent lamp ofthe ninth exemplary embodiment of the present invention is applied;

FIG. 17 illustrates a circuit diagram of an instant start-typeelectronic fluorescent lamp ballast to which the LED fluorescent lamp ofthe tenth exemplary embodiment of the present invention is applied;

FIG. 18 illustrates a circuit diagram of a soft start-type electronicfluorescent lamp ballast to which the LED fluorescent lamp of the fourthexemplary embodiment is applied;

FIG. 19 illustrates a circuit diagram of a soft start-type electronicfluorescent lamp ballast to which the LED fluorescent lamp of the sixthexemplary embodiment is applied;

FIG. 20 illustrates a circuit diagram of a soft start-type electronicfluorescent lamp ballast to which the LED fluorescent lamp of theseventh exemplary embodiment is applied;

FIG. 21 illustrates a circuit diagram of a soft start-type electronicfluorescent lamp ballast to which the LED fluorescent lamp of the tenthexemplary embodiment is applied;

FIG. 22 illustrates a circuit diagram of a starter lamp-based magneticfluorescent lamp ballast to which the LED fluorescent lamp of the fourthexemplary embodiment is applied;

FIG. 23 illustrates a circuit diagram of a starter lamp-based magneticfluorescent lamp ballast to which the LED fluorescent lamp of the sixthexemplary embodiment is applied;

FIG. 24 illustrates a circuit diagram of a starter lamp-based magneticfluorescent lamp ballast to which the LED fluorescent lamp of theseventh exemplary embodiment is applied;

FIG. 25 illustrates a circuit diagram of a starter lamp-based magneticfluorescent lamp ballast to which the LED fluorescent lamp of the tenthexemplary embodiment is applied;

FIG. 26 illustrates a circuit diagram of a rapid start-type magneticfluorescent lamp ballast to which the LED fluorescent lamp of the fourthexemplary embodiment is applied;

FIG. 27 illustrates a circuit diagram of a rapid start-type magneticfluorescent lamp ballast to which the LED fluorescent lamp of the sixthexemplary embodiment is applied;

FIG. 28 illustrates a circuit diagram of a rapid start-type magneticfluorescent lamp ballast to which the LED fluorescent lamp of theseventh exemplary embodiment is applied;

FIG. 29 illustrates a circuit diagram of an iron-core rapid start-typefluorescent lamp ballast to which the LED fluorescent lamp of the ninthexemplary embodiment is applied; and

FIG. 30 illustrates a circuit diagram of an iron-core rapid start-typefluorescent lamp ballast to which the LED fluorescent lamp of the tenthexemplary embodiment is applied.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will hereinafter be described in detail withreference to the accompanying drawings in which exemplary embodiments ofthe invention are shown.

The basic circuitries of electronic fluorescent lamp ballasts cangenerally be classified into a half bridge-type, instant start-type andprogram start-type. And conventional iron-core based magnetic ballastscan be classified into starter type and rapid start type. LEDfluorescent lamps according to exemplary embodiments of the presentinvention can be applied to nearly all types of fluorescent lampballasts. The structures of the LED fluorescent lamps according toexemplary embodiments of the present invention and the operations ofvarious types of fluorescent lamp ballasts to which the LED fluorescentlamps according to exemplary embodiments of the present invention areapplied will hereinafter be described in detail.

FIG. 1 illustrates a circuit diagram of an LED fluorescent lamp 110according to a first exemplary embodiment of the present invention.Referring to FIG. 1, the LED fluorescent lamp 110 may include an LEDarray 10, a plurality of capacitors C11 through C14, and a plurality ofexternal connection pins, i.e., first 111 through fourth 114. The LEDfluorescent lamp 110 may use only two of the first through fourthconnection pins 111 through 114. The LED fluorescent lamp 110 mayinclude two or more LED arrays 10 connected in parallel to each other.The structure of the LED fluorescent lamp 110 may be directly applied toLED fluorescent lamps according to other exemplary embodiments of thepresent invention.

The LED array 10 may include a plurality of LEDs (not shown) connectedin series, an anode terminal 10 a and a cathode terminal 10 b. Thecapacitor C11 may be connected between the anode terminal 10 a and thefirst connection pin 111, and the capacitor C12 may be connected betweenthe cathode terminal 10 b and the second connection pin 112. Thecapacitor C13 may be connected between the anode terminal 10 a and thethird connection pin 113, and the capacitor C14 may be connected betweenthe cathode terminal 10 a and the fourth connection pin 114.

The capacitors C11 through C14 may be connected to a half-bridge type ofelectronic ballast circuit via the first through fourth connection pins111 through 114 and may thus control the operating frequency of theseries resonant circuit which is composed of internal inductor andcapacitor of the ballast. Due to the variation of the operatingfrequency of the ballast, the impedance of the inductor inside theballast can be controlled and, as a result, the amount of current of LEDfluorescent lamp 110 can also be controlled. Thus, the basic structureof LED fluorescent lamp 110 may be applied to nearly all types offluorescent lamp ballasts.

FIG. 2 illustrates a circuit diagram of the LED array 10 shown inFIG. 1. Referring to FIG. 2( a), the LED array 10 may include aplurality of LEDs D1 through Dn connected in series.

In order to protect the LEDs D1 through Dn, the LED array 10 may alsoinclude a plurality of zener diodes Z1 through Zn connected in parallelto the LEDs D1 through Dn, respectively, in an opposite direction to thedirection in which the LEDs D1 through Dn are aligned, as shown in FIG.2( b). Referring to FIG. 2( b), if the applied voltage at 10 a ispositive with respect to 10 b, a current may flow through the LEDs D1through Dn. On the other hand, during a negative period of the input ACvoltage, a current may flow through the zener diodes Z1 through Zn. Theflow of a current through the zener diodes Z1 through Zn may become anineffective loss. Therefore, in order to prevent the flow of a reversecurrent through the zener diodes Z1 through Zn and thus to improveefficiency, various modifications may be made to the first exemplaryembodiment, and this will hereinafter be described in detail.

FIG. 3 illustrates a circuit diagram of an LED fluorescent lamp 120according to a second exemplary embodiment of the present invention. Thesecond exemplary embodiment is the same as the first exemplaryembodiment except that the LED fluorescent lamp 120 includes two diodesD21 and D22 connected in series to either end of an LED array 12. TheLED fluorescent lamp 120 may include only one of the diodes D21 and D22.The diodes D21 and D22 may allow a current to flow in the LED array 12only in a forward direction. Therefore, even if the LED array 12includes a plurality of zener diodes (not shown) connected in parallelto LEDs, it is possible to prevent power loss that may be caused by acurrent flown through the zener diodes during a negative period of aninput AC voltage.

FIG. 4 illustrates a circuit diagram of an LED fluorescent lamp 130according to a third exemplary embodiment of the present invention.Referring to FIG. 4, the LED fluorescent lamp 130 may include an LEDarray 13, first through fourth connection pins 131 through 134, aplurality of capacitors C31 through C34 connected to the first throughfourth connection pins 131 through 134, respectively, and a plurality ofdiodes D33 through D36 connected in parallel to the capacitors C31through C34, respectively. If the output terminals of a series-resonanttype of electronic ballast is connected to the connection pin pairs (131and 133) and (132 and 134) and a series-resonance sustain capacitorinside the electronic ballast is connected between the first and secondconnection pins 131 and 132 or between the third and fourth connectionpins 133 and 134 as shown in FIG. 12, the flow of a current in the LEDarray 13 may be controlled by the diodes D33 through D36 according tothe polarity of an input voltage provided by the electronic ballast. Forexample, if a positive voltage is applied to the third connection pin133 when the connection pin 134 is set as a reference point and theseries-resonance sustain capacitor is connected between the first andsecond connection pins 131 and 132, the capacitor C33 may becomeshort-circuited by the diode D35, the diodes D33 and D34 may becomeopen, and the capacitor C34 may become short-circuited by the diode D36.In this case, the initial resonant capacitance of the electronic ballastmay be equal to the total capacitance of the capacitor C31, theseries-resonance sustain capacitor C1 and the capacitor C32 in seriesand the resonant frequency of the ballast may be changed by thevariation of the resonant capacitance. In addition, if a negativevoltage is applied to the third connection pin 133, the capacitor C32may become short-circuited by the diode D34, and the capacitor C31 maybe short-circuited by the diode D33. In this case, the total capacitanceof the electronic ballast may be equal to the total capacitance of thecapacitor C34, the series-resonance sustain capacitor C1 and thecapacitor C33 in series.

FIG. 5 illustrates a circuit diagram of an LED fluorescent lamp 140according to a fourth exemplary embodiment of the present invention. Thefourth exemplary embodiment is the same as the third exemplaryembodiment except that the LED fluorescent lamp 140 also includes aplurality of diodes D47 through D50. Thus, the LED fluorescent lamp maybe able to stably operate keeping the characteristics of symmetricoperation regardless of variations in the phase of a voltage appliedthereto by a fluorescent lamp ballast.

FIG. 6 illustrates a circuit diagram of an LED fluorescent lamp 150according to a fifth exemplary embodiment of the present invention.Referring to FIG. 6, the LED fluorescent lamp 150 may include an LEDarray 15, first through fourth connection pins 151 through 154, aplurality of capacitors C51 through C54 connected to the first throughfourth connection pins 151 through 154, respectively, a plurality ofdiodes D53 through D56 connected in parallel to the capacitors C51through C54, respectively, and a plurality of resistors R51 through R54connected in parallel to the capacitors C51 through C54, respectively,for applying a current for an initial trigger operation of the ballast.

FIG. 7 illustrates a circuit diagram of an LED fluorescent lamp 160according to a sixth exemplary embodiment of the present invention.Referring to FIG. 7, the LED fluorescent lamp 160 may include an LEDarray 16, first through fourth connection pins 161 through 164, aplurality of capacitors C61 through C64 connected to the first throughfourth connection pins 161 through 164, respectively, and a plurality ofdiodes D63 through D66 connected in series to the capacitors C61 throughC64, respectively. The diodes D63 through D66 and a plurality of diodesD67 through D70 may allow the LED fluorescent lamp 160 to stably operatekeeping the characteristics of symmetric operation regardless of thephase of an AC voltage applied by a fluorescent lamp ballast.

FIG. 8 illustrates a circuit diagram of an LED fluorescent lamp 170according to a seventh exemplary embodiment of the present invention.

Referring to FIG. 8, the anode of a diode D73 may be connected to afirst connection pin 171, and the cathode of the diode D73 may beconnected to the anode of a diode D71. The anode of a diode D74 may beconnected to a second connection pin 172, and the cathode of the diodeD74 may be connected to the cathode of a diode D72. The anode of a diodeD75 may be connected to a third connection pin 173, and the cathode ofthe diode D75 may be connected to the anode of the diode D71. The anodeof a diode D76 may be connected to a fourth connection pin 174, and thecathode of the diode D76 may be connected to the cathode of the diodeD72. The anode of the diode D77 may be commonly connected to the cathodeof the diode D72 and second ends of capacitors C72 and C74, and thecathode of the diode D77 may be connected to an anode terminal 17 a ofan LED array 17. The anode of the diode D78 may be connected to acathode terminal 17 b of the LED array 17, and the cathode of the diodeD78 may be commonly connected to the anode of the diode D71 and secondends of capacitors C71 and C73.

The diodes D77 and D78 may allow the LED fluorescent lamp 170 to stablyoperate keeping the characteristics of symmetric operation regardless ofvariations in the phase of a voltage applied to the first through fourthconnection pins 171 through 174 by a fluorescent lamp ballast.

FIG. 9 illustrates a circuit diagram of an LED fluorescent lamp 180according to an eighth exemplary embodiment of the present invention.The eighth exemplary embodiment is the same as the seventh exemplaryembodiment except for the reverse direction of diodes D83 through D86which are connected in parallel to a plurality of capacitors C81 throughC84, respectively.

FIG. 10 illustrates a circuit diagram of an LED fluorescent lamp 190according to a ninth exemplary embodiment of the present invention.Referring to FIG. 10, the LED fluorescent lamp 190 may include firstthrough fourth connection pins 191 through 194, a plurality ofcapacitors C91 through C94 connected to the first through fourthconnection pins 191 through 194, respectively, and a plurality of diodesD93 through D96 connected in series to the capacitors C91 through C94,respectively. The LED fluorescent lamp 190 may also include a diode D97having an anode connected to a second end of an LED array 19 and acathode connected to the anode of the diode D93 and a diode D98 havingan anode connected to the cathode of the diode D94 and a cathodeconnected to a first end of the LED array 19.

The diodes D93 through D98 may allow the LED fluorescent lamp 190 tooperate in various types of fluorescent lamp ballasts regardless of thephase of an AC voltage.

FIG. 11 illustrates a circuit diagram of an LED fluorescent lamp 200according to a tenth exemplary embodiment of the present invention. TheLED fluorescent lamp 200 is almost the same as the LED fluorescent lamp190 shown in FIG. 10 except that it also includes diodes D109 and D110.More specifically, referring to FIG. 11, the anode of the diode D109 maybe connected to the cathode of a diode D106, and the cathode of thediode D109 may be connected to a first end of an LED array 20. The anodeof the diode D110 may be connected to a second end of the LED array 20,and the cathode of the diode D110 may be connected to the anode of thediode D105. The diodes D109 and D110 may allow the LED fluorescent lamp200 to operate symmetrically in response to a voltage applied thereto byan external voltage source.

The basic structures of the LED fluorescent lamps 110 through 200 of thefirst through tenth exemplary embodiments can be applied to nearly mosttypes of fluorescent lamp ballasts. The operations of various types offluorescent lamp ballasts will hereinafter be described in detail,taking the LED fluorescent lamps 140, 160, 170, 190 and 200 of thefourth, sixth, seventh, ninth and tenth exemplary embodiments as anexample.

FIG. 12 illustrates a circuit diagram of a half-bridge-type offluorescent lamp ballast to which the LED fluorescent lamp 140 of thefourth exemplary embodiment is applied.

In a half-bridge type of electronic fluorescent lamp ballast, aseries-resonant circuit including an inductor and a capacitor may beconnected to a switching output node of a half-bridge inverter composedof a semiconductor switching device. The half-bridge type of electronicballast may initially ignite a fluorescent lamp using a series-resonancevoltage applied to either end of the resonant capacitor. Once thefluorescent lamp is discharged, the main current flown in thefluorescent lamp will be controlled by the impedance of an inductor ofthe series-resonant circuit. Referring to FIG. 12, the resonantfrequency of a series-resonant circuit and the operating frequency ofswitching devices Q61 and Q62 may be synchronized with each other by acurrent transformer To. Power consumption Ps may be defined by Equation(1):Ps≅IsVs  (1)where Vs indicates a direct current (DC) input voltage and Is indicatesan average current applied to an inverter.

A load current may be the same as the average current Is. Thus, ifC₀>>C1, C₀>>C41˜C44, and if we let the total capacitance of the LED lamp(140) with the capacitor C1 inside the ballast to Ca then the averagecurrent Is may be defined using Equations (2) through (4):

$\begin{matrix}{{{Is} \simeq {{fCQ}_{0}{Vs}}};} & (2) \\{{C = {\frac{2C_{0}C_{a}}{C_{a} + {2C_{0}}} \simeq C_{a}}};{and}} & (3) \\{Q_{0} = {\frac{1}{R_{0}}\sqrt{L_{0}/C}}} & (4)\end{matrix}$

where f indicates the operating frequency of the switching devices Q61and Q62 and Ro indicates the internal resistance of the LED fluorescentlamp 140 when the LED fluorescent lamp 140 is operating at a resonantfrequency.

An operating frequency f of an inverter may be defined by Equations (5):

$\begin{matrix}{{f = {\frac{\omega}{2\pi} = {\frac{\omega_{0}}{2\pi}\sqrt{1 - {{1/4}Q_{0}^{2}}}}}}{\omega_{0} = {1/{\sqrt{L_{0}C}.}}}} & (5)\end{matrix}$

Therefore, the average current Is may be calculated using Equations (2)and (5), as indicated by Equation (6):

$\begin{matrix}\begin{matrix}{I_{S} \simeq {\frac{1}{2\pi}\omega_{0}{CQ}_{0}V_{s}\sqrt{1 - {{1/4}Q^{2}}}}} \\{{\simeq {\frac{Q_{0}V_{S}}{2\pi\; Z}\sqrt{1 - {{1/4}Q^{2}}}}};}\end{matrix} & (6)\end{matrix}$

where Z indicates impedance. The impedance Z may be defined by Equation(7):

$\begin{matrix}{Z = {{\omega_{0}L_{0}} = {\frac{1}{\omega_{0}C} = {\sqrt{L_{0}/C}.}}}} & (7)\end{matrix}$

If C₀>>C1, the operating frequency f may be determined by the totalcapacitance C_(a). Therefore, once the LED fluorescent lamp 140 isconnected to a half-bridge type of electronic ballast, the half-bridgeinverter may operate as follows. Referring to FIG. 12, at initialresonance stage, if the switching device Q61 is turned on and thus thevoltage Vs is applied to a node A, a resonance current may flow,sequentially passing through Lo, D45, C41, C1, C42, D46, and 2Co. On theother hand, if the switching device Q62 is turned on, the voltage at thenode A may become a ground voltage, and the resonance current may flowalong an opposite path to the path of the resonant current, 2Co, C44,D44, C1, D43, C43 and Lo.

To guarantee the general usage of the LED fluorescent lamp 140, thebasic structure of LED fluorescent lamp 140 must be symmetrical. Thus,the first through fourth connection pins 141 through 144 of the LEDfluorescent lamp 140 must not have any polarity. Therefore, atseries-resonant condition, if C41=C42=C43=C44=C₂, the total capacitanceCa may be defined by Equation (8):

$\begin{matrix}{C_{a} = {\frac{C_{1}C_{2}}{{2C_{1}} + C_{2}}.}} & (8)\end{matrix}$

Therefore, if C₂<<C₁, Ca≈C₂/2 and the impedance Z may increase.Accordingly, a current flown in the LED fluorescent lamp 140 maydecrease, and thus, it is possible to properly control the current flownin the LED fluorescent lamp 140. Thus, it is possible to install the LEDfluorescent lamp 140 in a half-bridge type of electronic fluorescentlamp ballast without the need to re-wiring the fluorescent lamp fixture.

FIG. 13 illustrates a circuit diagram of an instant start-typeelectronic fluorescent lamp ballast to which the LED fluorescent lamp140 of the fourth exemplary embodiment is applied. Referring to FIG. 13,due to a self-oscillation operation of a circuit including transformersT1 and T2 and a capacitor C, switching devices Q71 and Q72 may be ableto continue a switching operation. The transformer T2 may be connectedbetween a switching node A and a node B by a primary winding T2-1. Theinstant start-type of electronic fluorescent lamp ballast may initiallydischarge the fluorescent lamp using a high voltage induced to asecondary winding T2-2 of the transformer T2. Once the fluorescent lampis discharged, the instant start-type of electronic ballast may controlthe stabilization current with the use of a capacitor C1, which isconnected in series to a lamp load.

The operation of the instant start-type of electronic ballast operatingwith LED fluorescent lamp 140 will hereinafter be described in furtherdetail. The transformer T2 may resonate with the self-oscillationfrequency and may thus induce a high AC voltage to the secondary windingT2-2. If the voltage at the node C is positive with respect to thevoltage at the node D, a current may flow, sequentially passing throughthe node C, the capacitor C₁, the diode D43, the diode D41, the LEDarray 14, the diode D42, the diode D44 and the node D. On the otherhand, if the voltage at the node C is negative with respect to thevoltage at the node D, a current may flow, sequentially passing throughthe node D, the diode D48, the diode D41, the LED array 14, the diodeD42, the diode D47, the capacitor C₁ and the node C. Alternatively, acurrent may flow, sequentially passing through the node D, the capacitorC42, the diode D47, the capacitor C₁, and the node C or the node D, thediode D48, the capacitor C41, the capacitor C₁, and the node C dependingupon the total number of LEDs.

Therefore, the main current flown in the LED array 14 may be controlledby the value of the impedance of the capacitor C1, that is, 1/jΩC1 ofthe instant start-type ballast and the total number of series-connectedLEDs of LED array 14.

FIG. 14 illustrates a circuit diagram of an instant start-typeelectronic fluorescent lamp ballast to which the LED fluorescent lamp160 of the sixth exemplary embodiment is applied. Referring to FIG. 14,when the instant start-type electronic fluorescent lamp ballast isconnected to the first and second connection pins 161 and 162 of the LEDfluorescent lamp 160, a transformer T2 may resonate withself-oscillation frequency and may thus induce a high AC voltage to asecondary winding T2-2. If the voltage at the node C is positive withrespect to the voltage at the node D, a current may flow, sequentiallypassing through the node C, the capacitor C₁, the capacitor C61, thediode D63, the diode D61, the LED array 16, the diode D62, the diodeD64, the capacitor C62 and the node D with a phase being shifted by π/2by the capacitance of the capacitors C101 through C104.

On the other hand, if the voltage at the node C is negative with respectto the voltage at the node D, a current may flow, sequentially passingthrough the node D, the capacitor C62, the diode D68, the diode D61, theLED array 16, the diode D62, the diode D67, the capacitor C61, thecapacitor C₁ and the node C with a phase being shifted by π/2 by thecapacitance of the capacitors C101 through C104.

Therefore, the main current flown in the LED array 16 may be controlledby the total composite impedance of the series-connected capacitors C₁,C61 and C62. Therefore, it is possible to control a current flown in anLED array load by varying the capacitances of the capacitors C61 and C62in the LED fluorescent lamp 160.

If we let C61=C62=C₂, the composite impedance Z may be defined byEquation (9):

$\begin{matrix}{Z = {{{- j}\;\frac{1}{\omega\; C_{1}}} - {j{\frac{2}{\omega\; C_{2}}.}}}} & (9)\end{matrix}$

The third and fourth connection pins 163 and 164 of the LED fluorescentlamp 160 may be provided in order to make the LED fluorescent lamp 160operate symmetrically not having any polarity. The operation of aninstant start-type electronic fluorescent lamp ballast when the ballastis connected to the third and fourth connection pins 163 and 164 may bebasically the same as the operation when the ballast is connected to thefirst and second connection pins 161 and 162.

FIG. 15 illustrates a circuit diagram of an instant start-typeelectronic fluorescent lamp ballast to which the LED fluorescent lamp170 of the seventh exemplary embodiment is applied. Referring to FIG.15, switching devices Q71 and Q72 continue a switching operation by theself-oscillation operation of the circuit composed of transformers T1,T2 and a capacitor C. Primary winding T2-1 of the transformer T2 isconnected between the switching point A and the center point of theseries-connected capacitors Co and a high AC voltage may be induced atthe secondary winding T2-2. If the voltage at the node C is positivewith respect to the voltage at the node D, a current may flow,sequentially passing through the node C, the capacitor C1, the diodeD73, the diode D71, the LED array 17, the diode D72, the capacitor C72and the node D. On the other hand, if the voltage at the node C isnegative with respect to the voltage at the node D, a current may flow,sequentially passing through the node D, the diode D74, the diode D77,the LED array 17, the diode D78, the capacitor C71, the capacitor C1 andthe node C.

The operation of an instant start-type electronic fluorescent lampballast to which the LED fluorescent lamp 180 shown in FIG. 9 is appliedis almost the same as the operation of the instant start-type electronicfluorescent lamp ballast shown in FIG. 15. More specifically, in theinstant start-type electronic fluorescent lamp ballast having the LEDfluorescent lamp 180, if a positive voltage is applied to the firstconnection pin 181 of the LED fluorescent lamp 180 and a negativevoltage is applied to the second connection pin 182 of the LEDfluorescent lamp, i.e., if the voltage at a node C is positive withrespect to the voltage at a node D, a current may flow, sequentiallypassing through the node C, the capacitor C1, the capacitor C81, thediode D81, the LED array 18, the diode D82, the diode D84 and the nodeD. On the other hand, if a negative voltage is applied to the firstconnection pin 181 and a positive voltage is applied to the secondconnection pin 182, i.e., if the voltage at the node C is negative withrespect to the voltage at the node D, a current may flow, sequentiallypassing through the node D, the capacitor C82, the diode D87, the LEDarray 18, the diode D88, the diode D83, the capacitor C1 and the node C.

In short, the operation of an instant start-type electronic fluorescentlamp ballast to which the LED fluorescent lamp 180 of the eighthexemplary embodiment is applied is almost the same as the operation ofan instant start-type electronic fluorescent lamp ballast to which theLED fluorescent lamp 170 of the seventh exemplary embodiment is applied,except for the path of a current.

FIG. 16 illustrates a circuit diagram of an instant start-typeelectronic fluorescent lamp ballast to which the LED fluorescent lamp190 of the ninth exemplary embodiment of the present invention isapplied, and FIG. 17 illustrates a circuit diagram of an instantstart-type electronic fluorescent lamp ballast to which the LEDfluorescent lamp 200 of the tenth exemplary embodiment of the presentinvention is applied.

Referring to FIG. 16, when the output wires of the electronicfluorescent lamp ballast are connected to the first and secondconnection pins 191 and 192, a transformer T2 may resonate withself-oscillation frequency and may thus induce a high AC voltage to asecondary winding T2-2. If the voltage at the node C is positive withrespect to the voltage at the node D, a current may flow, sequentiallypassing through the node C, the capacitor C₁, the capacitor C91, thediode D93, the diode D91, the LED array 19, the diode D92, the diodeD94, the capacitor C92 and the node D, with a phase being shifted by π/2by the capacitances of the capacitors C91 through C94. On the otherhand, if the voltage at the node C is negative with respect to thevoltage at a node D, a current may flow, sequentially passing throughthe node D, the capacitor C92, the diode D98, the LED array 19, thediode D97, the capacitor C91, the capacitor C₁, and the node C, with aphase being shifted by π/2 by the capacitances of the capacitors C91through C94.

Referring to FIG. 17, the third and fourth connection pins 203 and 204may be provided in order for the LED fluorescent lamp 200 to operatesymmetrically. The operation of the electronic fluorescent lamp ballastshown in FIG. 17 is almost the same as the operation of the electronicfluorescent lamp ballast shown in FIG. 16.

FIG. 18 illustrates a circuit diagram of a soft start-type electronicfluorescent lamp ballast to which the LED fluorescent lamp 140 of thefourth exemplary embodiment is applied. Referring to FIG. 18, a seriesresonant circuit including an inductor T3 and a capacitor C1 may beconnected between switching node A, switching point of switching devicesQ81 and Q82, and ground point, and the LED fluorescent lamp 140 may beconnected to both ends of the capacitor C1. Originally, the secondarywindings of inductor T3-a and T3-b are intended for preheating thefilament of fluorescent lamp in order to maximize the lifetime of thefluorescent lamp by minimizing the dissipation of the oxide componentscoated on the filament of the fluorescent lamp. But when this softstart-type of electronic ballast drives the LED fluorescent lamp, thissecondary windings should not influence an abnormal effect upon thenormal operation of the LED fluorescent lamp 180.

If the operating frequency f of the switching devices Q81 and Q82 issynchronized with the resonant frequency which is composed of inductanceL1 of the inductor T3 and the capacitance C1 and if we suppose C0>>C1,the operating frequency f may be defined by Equation (10):f=½π√{square root over (L ₁ C ₁)}  (10).

A high AC voltage with the operating frequency f may be induced to bothends of the capacitor C1. Since the secondary windings T3-a and T3-b arecoupled to the inductor T3, during a positive period of the AC voltageinduced to T3-a, a preheating current may flow, sequentially passingthrough a capacitor Ca, the diode D43 and the capacitor C43. On theother hand, during a negative period of the AC voltage, a preheatingcurrent may flow, sequentially passing through the diode D45, thecapacitor C41 and the capacitor Ca. Similarly during a positive periodof the AC voltage induced to T3-b, a preheating current may flow,sequentially passing through the capacitor C44, the diode D44 and thecapacitor Cb. On the other hand, during a negative period of the ACvoltage, a preheating current may flow, sequentially passing through thecapacitor Cb, the capacitor C42 and the diode D46. If we letC41=C42=C43=C44=C₂, the total capacitance C that controls the preheatingcurrent flown in the secondary winding T3-a or T3-b may be defined byEquation (11):

$\begin{matrix}{C = {\frac{C_{a}C_{2}}{C_{a} + C_{2}}.}} & (11)\end{matrix}$

Since Ca>>C₂, the current flown in the secondary windings T3-a or T3-bmay be determined by capacitance C₂, which is equal to the value ofcapacitor C41 through C44. Since the capacitance C₂ is only as small asseveral thousands of pico-farads and the voltage induced to thesecondary windings T3-a or T3-b are only as low as several volts, thecurrent flown through the secondary windings T3-a or T3-b may be ignoredby the diodes D43 through D46.

If the resonant voltage induced at the node B is positive with respectto the voltage at the node C, a current may flow in the LED fluorescentlamp 140, sequentially passing through the node B, the diode D45, thediode D41, the LED array 14, the diode D42, and the diode D46. On theother hand, if the voltage at the node B is negative with respect to thevoltage at the node C, a current may flow in the LED fluorescent lamp140, sequentially passing through the node C, the diode D49, the diodeD41, the LED array 14, the diode D42, the diode D50 and the node B.

The main current flown in the LED array 14 may be controlled by varyingthe number of series connected LEDs.

FIG. 19 illustrates a circuit diagram of a soft start-type electronicfluorescent lamp ballast to which the LED fluorescent lamp 160 of thesixth exemplary embodiment is applied. Referring to FIG. 19, anoperating frequency f may be the same as that described above withreference to FIG. 18, and an AC voltage with the operating frequency fmay be induced to both ends of a capacitor C1. During the operation ofthe soft start-type electronic fluorescent lamp ballast with LEDfluorescent lamp instead of conventional fluorescent lamp, since thevoltage induced to a secondary winding T3-a, which is coupled to aninductor T3 and is designed for pre-heating the filaments of fluorescentlamp, is only as low as below 10 V, the voltage at the secondary windingT3-a may be blocked by the diodes D63 and D65, and thus, a preheatingcurrent for fluorescent lamp filament may not be able to flow throughthe secondary winding T3-a. Likewise, the voltage at the secondarywinding T3-b for preheating the fluorescent lamp filament may be blockedby the diodes D64 and D66, and thus, a preheating current forfluorescent lamp filament may not be able to flow through the windingT3-b. Therefore, power loss that may be caused by the secondary windingT3-a and T3-b may be ignored and as a result, the current for filamentpreheating generated by the secondary windings T3-a and T3-b may beignored.

If we ignore the secondary windings T3-a and T3-b, when the voltage atthe node B is positive with respect to the voltage at the node C, acurrent may flow, sequentially passing through the node B, the capacitorC63, the diode D65, the diode D61, the LED array 16, the diode D62, thediode D66, the capacitor C64 and the node C. On the other hand, if thevoltage at the node B is negative with respect to the voltage at thenode C, a current may flow, sequentially passing through the node C, thecapacitor C64, the diode D69, the diode D61, the LED array 16, the diodeD62, the diode D70, the capacitor C63 and the node B. Therefore, if welet C61=C62=C63=C64=C₂, the composite impedance of the soft start-typeelectronic fluorescent lamp ballast may become 2/jΩC2. Thus, the maincurrent flown in the LED array 16 may be controlled by varying thecapacitance C2 of the capacitors C61 through C64.

FIG. 20 illustrates a circuit diagram of a soft start-type electronicfluorescent lamp ballast to which the LED fluorescent lamp 170 of theseventh exemplary embodiment is applied. The basic operation of the softstart-type electronic ballast shown in FIG. 20 is almost the same as theoperation of the soft start-type electronic ballast shown in FIG. 19.

Referring to FIG. 20, a current flown into the LED array 17 by secondarywindings T3-a and T3-b for pre-heating the fluorescent lamp filamentsmay be low enough to be ignored. If we ignore the secondary windingsT3-a and T3-b, when the voltage at the node B is positive with respectto the voltage at the node C, a current may flow, sequentially passingthrough the node B, the diode D75, the diode D71, the LED array 17, thediode D72, the capacitor C74 and the node C. On the other hand, if thevoltage at the node B is negative with respect to the voltage at thenode C, a current may flow, sequentially passing through the node C, thediode D76, the diode D77, the LED array 17, the diode D78, the capacitorC73 and the node B. Therefore, if we let C71=C72=C73=C74=C₂, the totalcomposite impedance of the soft start-type electronic fluorescent lampballast may become 1/jΩC₂. Thus, the main current flown in the LED array17 may also be controlled by varying the capacitance C₂ and the totalnumber of LEDs.

FIG. 21 illustrates a circuit diagram of a soft start-type electronicfluorescent lamp ballast to which the LED fluorescent lamp 200 of thetenth exemplary embodiment is applied. Referring to FIG. 21, a currentflown into the LED array 20 by secondary windings T3-a and T3-b forpre-heating filaments may be low enough to be ignored. If we ignore thesecondary windings T3-a and T3-b, when the voltage at the node B ispositive with respect to the voltage at the node C, a current may flow,sequentially passing through the node B, the capacitor C103, the diodeD105, the diode D101, the LED array 20, the diode D102, the diode D106,the capacitor C104 and the node C, with a phase being shifted by Tr/2 bythe capacitance of the capacitors C101 through C104.

On the other hand, if the voltage at the node B is negative with respectto the voltage at the node C, a current may flow, sequentially passingthrough the node C, the capacitor C104, the diode D109, the LED array20, the diode D110, the capacitor C103 and the node B, with a phasebeing shifted by π/2 by the capacitance of the capacitors C101 throughC104. Therefore, if we let C101=C102=C103=C104=C₂, the total compositeimpedance of the soft start-type electronic fluorescent lamp ballast maybecome 2/jΩC₂ and the main current flown in the LED array 20 may becontrolled by varying the capacitance C₂ of capacitors C101 throughC104.

FIG. 22 illustrates a circuit diagram of a starter lamp-based magneticfluorescent lamp ballast to which the LED fluorescent lamp 140 of thefourth exemplary embodiment is applied. Referring to FIG. 22, when wedrive the LED fluorescent lamp instead of conventional fluorescent lamp,a starter lamp (S) 300 may be considered to be open, and thus, during apositive period of an input AC voltage, a current may flow, sequentiallypassing through an inductor L, the diode D45, the diode D41, the LEDarray 14, the diode D42 and the diode D46. In this case, the maincurrent flown in the LED fluorescent lamp 140 may be controlled by theimpedance of the inductor L, i.e., jΩL and the total number of LEDs.

On the other hand, during a negative period of the input AC inputvoltage, a current may flow, sequentially passing through the diode D49,the diode D41, the LED array 14, the diode D42, the diode D50 and theinductor L. In this case, the current flown in the LED fluorescent lamp140 may be a pulsating current having twice as high a frequency(100/120Hz) as the frequency f(50/60 Hz) of the commercial electric powersource. Therefore, it is possible to considerably reduce the probabilityof occurrence of flickering, which may be caused by driving the LEDfluorescent lamp 140 at the frequency f of the commercial electric powersource.

FIG. 23 illustrates a circuit diagram of a starter lamp-based magneticfluorescent lamp ballast to which the LED fluorescent lamp 160 of thesixth exemplary embodiment is applied. Referring to FIG. 23, when wedrive the LED fluorescent lamp instead of conventional fluorescent lamp,a starter lamp (S) 300 may be considered to be open, and thus, during apositive period of an input AC input voltage, a current may flow,sequentially passing through the capacitor C63, the diode D65, the diodeD61, the LED array 16, the diode D62, the diode D66, and the capacitorC64, with a phase being shifted by π/2 by the capacitance of thecapacitors C61 through C64.

On the other hand, during a negative period of the input AC inputvoltage, a current may flow, sequentially passing through the capacitorC64, the diode D69, the diode D61, the LED array 16, the diode D62, thediode D70, and the capacitor C63 with a phase being shifted by π/2 bythe capacitance of the capacitors C61 through C64.

If we let C61=C62=C63=C64=C₂, total composite impedance Z that controlsthe main current flown in the LED fluorescent lamp 160 may be defined byEquation (12):

$\begin{matrix}{Z = {{j\;\omega\; L} - {j\;\frac{2}{\omega\; C_{2}}}}} & (12)\end{matrix}$where L indicates the inductance of an inductor L.

The current flown in the LED fluorescent lamp 160 may be a pulsatingcurrent having twice as high a frequency(100/120 Hz) as the frequencyf(50/60 Hz) of the commercial electric power source. Therefore, it ispossible to considerably reduce the probability of occurrence offlickering, which may be caused by driving the LED fluorescent lamp 140at the frequency f.

FIG. 24 illustrates a circuit diagram of a starter lamp-based magneticfluorescent lamp ballast to which the LED fluorescent lamp 170 of theseventh exemplary embodiment is applied. Referring to FIG. 24, during apositive period of an input AC input voltage, a current may flow,sequentially passing through the diode D75, the diode D71, the LED array17, the diode D72 and the capacitor C74. On the other hand, during anegative period of the input AC input voltage, a current may flow,sequentially passing through the diode D76, the diode D77, the LED array17, the diode D78 and the capacitor C73.

If we let C71=C72=C73=C74=C₂, total composite impedance Z that controlsthe main current flown in the LED fluorescent lamp 170 may be defined byEquation (13):

$\begin{matrix}{Z = {{j\;\omega\; L} - {j\;\frac{1}{\omega\; C_{2}}}}} & (13)\end{matrix}$where L indicates the inductance of an inductor.

FIG. 25 illustrates a circuit diagram of a starter lamp-type magneticfluorescent lamp ballast to which the LED fluorescent lamp 200 of thetenth exemplary embodiment is applied. Referring to FIG. 25, when wedrive the LED fluorescent lamp instead of conventional fluorescent lamp,a starter lamp (S)300 may be considered to be open and thus during apositive period of the input AC input voltage, a current may flow,sequentially passing through the capacitor C103, the diode D105, thediode D101, the LED array 20, the diode D102, the diode D106, and thecapacitor C104, with a phase being shifted by π/2 by the capacitance ofthe capacitors C101 through C104.

On the other hand, during a negative period of the AC input voltage, acurrent may flow, sequentially passing through the capacitor C104, thediode D109, the LED array 20, the diode D110, the capacitor C103, with aphase being shifted by π/2 by the capacitance of the capacitors C101through C104. If we let C101=C102=C103=C104=C₂, total compositeimpedance Z that controls the main current flown in the LED fluorescentlamp 200 may also be defined by equation (12).

FIG. 26 illustrates a circuit diagram of a magnetic rapid start-typefluorescent lamp ballast to which the LED fluorescent lamp 140 of thefourth exemplary embodiment is applied. Referring to FIG. 26, if wedefine the voltages for preheating the filaments of fluorescent lampinduced to the secondary windings n1 and n2 as Vn1 and Vn2,respectively, during a positive period of the voltage Vn1, that is, whenthe voltage applied to the node C is positive with respect to the nodeA, the capacitor C41 may be short-circuited by the diode D43, and thus,the load of the secondary winding n1 may become equal to the capacitanceof the capacitor C42, and during a negative period of the voltage Vn1,the capacitor C43 may be short-circuited by the diode D45, and thus, theload of the secondary winding n1 may become equal to the capacitance ofthe capacitor C41.

Likewise, during a positive period of the voltage Vn2, that is, when thevoltage applied to the node B is positive with respect to the node D,the load of the winding n2 may become equal to the capacitance of thecapacitor C44, and during a negative period of the voltage Vn2, that is,when the voltage applied to the node D is positive with respect to nodeB, the load of the winding n2 may become equal to the capacitance of thecapacitor C42.

To keep the symmetric characteristics of fluorescent lamp, the firstthrough fourth connection pins 141 through 144 of the LED fluorescentlamp 140 should not have any polarity. For this purpose, the capacitorsC41 through C44 should be designed to have the same capacitance value.If we let this value as C₂, since the capacitance C₂ is only as low asseveral thousands of pico-farads, the composite impedance, i.e., 1/jΩC₂,may become very high at the frequency of 50-60 Hz. Therefore, thepreheating current of the secondary windings n1 and n2 may be ignored.

An output voltage Vo applied to node A and node B may be defined byEquation (14):

$\begin{matrix}{{Vo} = {\frac{{n\; 3} + {n\; 4}}{n\; 4}{Vi}}} & (14)\end{matrix}$

where Vi indicates the input voltage from the commercial electric powersource.

When the voltage at the node A is positive with respect to the voltageat the node B, a current may flow in the LED fluorescent lamp 140,sequentially passing through the node C, the diode D43, the diode D41,the LED array 14, the diode D42, the diode D44 and the node D. On theother hand, if the voltage at the node C is negative with respect to thevoltage at the node D, a current may flow in the LED fluorescent lamp140, sequentially passing through the node D, the diode D48, the diodeD41, the LED array 14, the diode D42, the diode D47 and the node C. Themain current flown in the LED array 14 may be controlled by theimpedance of the leakage inductance of the ballast jΩL1 and the totalnumber of series connected LEDs.

In case of magnetic rapid start-type fluorescent lamp ballast, like inthe starter lamp-based magnetic fluorescent lamp ballast shown in FIG.25, the main current flown in the LED fluorescent lamp 140 may be apulsating current having twice as high a frequency (100/120 Hz) as thefrequency f (50/60 Hz) of the commercial electric power source.Therefore, it is possible to considerably reduce the probability ofoccurrence of flickering, which may be caused by driving the LEDfluorescent lamp 140 at the frequency f of commercial electric powersource.

FIG. 27 illustrates a circuit diagram of a magnetic rapid start-typefluorescent lamp ballast to which the LED fluorescent lamp 160 of thesixth exemplary embodiment is applied. Referring to FIG. 27, if thevoltage at the node A is positive with respect to the voltage at thenode B, a current may flow, sequentially passing through the node C, thecapacitor C61, the diode D63, the diode D61, the LED array 16, the diodeD62, the diode D64, the capacitor C62, and the node D, with a phasebeing shifted by π/2 by the capacitance of the capacitors C61 throughC64.

On the other hand, if the voltage at the node A is negative with respectto the voltage at the node B, a current may flow, sequentially passingthrough the node D, the capacitor C62, the diode D68, the diode D61, theLED array 16, the diode D62, the diode D67, the capacitor C61, and thenode C, with a phase being shifted by π/2 by the capacitance of thecapacitors C61 through C64.

If we let C61=C62=C63=C64=C₂, total composite impedance Z that controlsthe main current flown in the LED fluorescent lamp 160 may be defined byEquation (15):

$\begin{matrix}{Z = {{j\;\omega\; L_{1}} - {j\;\frac{2}{\omega\; C_{2}}}}} & (15)\end{matrix}$

where L1 indicates leakage inductance of the ballast.

FIG. 28 illustrates a circuit diagram of a magnetic rapid start-typefluorescent lamp ballast to which the LED fluorescent lamp 170 of theseventh exemplary embodiment is applied. Referring to FIG. 28, if thevoltage at the node A is positive with respect to the voltage at thenode B, a current may flow, sequentially passing through the node C, thediode D73, the diode D71, the LED array 17, the diode D72, the capacitorC72, and the node D. On the other hand, if the voltage at the node A isnegative with respect to the voltage at the node B, a current may flow,sequentially passing through the node D, the diode D74, the diode D77,the LED array 17, the diode D78, the capacitor C71, and the node C.

If we let C71=C72=C73=C74=C₂, total composite impedance Z that controlsthe main current flown in the LED fluorescent lamp 170 may be defined byEquation (16):

$\begin{matrix}{Z = {{j\mspace{2mu}\omega\; L_{1}} - {j\;\frac{1}{\omega\; C_{2}}}}} & (16)\end{matrix}$

where L1 indicates leakage inductance of the ballast.

In this case, the current flown through the LED fluorescent lamp 170 maybe a pulsating current having twice as high a frequency(100/120 Hz) asthe frequency f (50/60 Hz) of the commercial electric power source.

FIG. 29 illustrates a circuit diagram of an iron core rapid start-typefluorescent lamp ballast to which the LED fluorescent lamp 190 of theninth exemplary embodiment is applied, and FIG. 30 illustrates a circuitdiagram of an iron core rapid start-type fluorescent lamp ballast towhich the LED fluorescent lamp 200 of the tenth exemplary embodiment isapplied.

Referring to FIG. 29, if the voltage at the node A is positive withrespect to the voltage at the node B, a current may flow, sequentiallypassing through the node C, the capacitor C91, the diode D93, the diodeD91, the LED array 19, the diode D92, the diode D94, the capacitor C92,and the node D, with a phase being shifted by π/2 by the capacitance ofthe capacitors C91 through C94.

On the other hand, if the voltage at the node A is negative with respectto the voltage at the node B, a current may flow, sequentially passingthrough the node D, the capacitor C92, the diode D98, the LED array 19,the diode D97, the capacitor C91 and the node C, with a phase beingshifted by π/2 by the capacitance of the capacitors C91 through C94.

The operation of the magnetic rapid start-type fluorescent lamp ballastshown in FIG. 30 is almost the same as the operation of the magneticrapid start-type fluorescent lamp ballast shown in FIG. 29 except thattwo diodes D109 and D110 are added to keep the symmetric characteristicsof LED fluorescent lamp 200.

The LED fluorescent lamps according to exemplary embodiments of thepresent invention can be readily installed and used with various typesof electronic fluorescent lamp ballast.

The LED fluorescent lamp according to the present invention is notrestricted to the exemplary embodiments set forth herein. Therefore,variations and combinations of the exemplary embodiments set forthherein may fall within the scope of the present invention.

As described above, the LED fluorescent lamp according to the presentinvention can be readily installed and used with various types offluorescent lamp ballasts without the requirement of the installation ofan additional fluorescent lamp ballasts or the change of internal wiringof the fixture. Therefore, the LED fluorescent lamp according to thepresent invention can replace an existing fluorescent lamp veryefficiently at low cost.

While the present invention has been particularly been particularlyshown and described with reference to exemplary embodiments thereof, itwill be understood by those of ordinary skill in the art that variouschanges in form and details may be made therein without departing fromthe spirit and scope of the present invention as defined by thefollowing claims.

What is claimed is:
 1. A light-emitting diode (LED) lamp comprising:four external connection pins having at least two connection pinsconnected to an electronic or magnetic fluorescent lamp ballast; an LEDarray including a plurality of LEDs in series; one or more capacitorsconnected between the LED array and the external connection pins, theone or more capacitors varying an impedance of the electronic ormagnetic fluorescent lamp ballast connected to the LED lamp through theexternal connection pins; and one or more diodes, each of said one ormore diodes being connected in parallel with corresponding one of saidone or more capacitors.
 2. The LED lamp of claim 1, wherein the one ormore capacitors include a first capacitor having a first end connectedto a terminal of the electronic or magnetic fluorescent lamp ballastthrough a first connection pin and a second end connected to an anodeterminal of the LED array, and a second capacitor having a first endconnected to another terminal of the electronic or magnetic fluorescentlamp ballast through a second connection pin and a second end connectedto a cathode terminal of the LED array, and wherein the one or morediodes include a first diode having an anode connected to the first endof the first capacitor and a cathode connected to the second end of thefirst capacitor, and a second diode having a cathode connected to thefirst end of the second capacitor and an anode connected to the secondend of the second capacitor.
 3. The LED lamp of claim 2, wherein the oneor more capacitors further include a third capacitor having a first endconnected to the third connection pin and a second end connected to theanode terminal of the LED array, and wherein the one or more diodesfurther include a third diode having an anode connected to the first endof the third capacitor and a cathode connected to the second end of thethird capacitor.
 4. The LED lamp of claim 3, wherein the one or morecapacitors further include a fourth capacitor having a first endconnected to the fourth connection pin and a second end connected to thecathode terminal of the LED array, and wherein the one or more diodesfurther include a fourth diode having a cathode connected to the firstend of the fourth capacitor and an anode connected to the second end ofthe fourth capacitor.
 5. The LED lamp of claim 4, further comprising: afifth diode having an anode connected to the anode of the second diodeand a cathode connected to the first connection pin; a sixth diodehaving an anode connected to the second connection pin and a cathodeconnected to the cathode of the first diode; a seventh diode having ananode connected to the fourth connection pin and a cathode connected tothe cathode of the third diode; and an eighth diode having an anodeconnected to the anode of the fourth diode and a cathode connected tothe third connection pin.
 6. An LED lamp comprising: an LED arrayincluding a plurality of LEDs connected in series; first through fourthconnection pins; first through fourth capacitors, each of first ends ofthe first through fourth capacitors connected to the first throughfourth connection pins, respectively; a first diode having an anodeconnected to a second end of the first capacitor and a cathode connectedto a first end of the led array; a second diode having an anodeconnected to a second end of the LED array and a cathode connected to asecond end of the second capacitor; a third diode having an anodeconnected to a second end of the third capacitor and a cathode connectedto the first end of the led array; a fourth diode having an anodeconnected to the second end of the LED array and a cathode connected toa second end of the fourth capacitor; a fifth diode having an anodeconnected to the second end of the LED array and a cathode connected tothe second end of the first capacitor; and a sixth diode having an anodeconnected to the second end of the second capacitor and a cathodeconnected to the first end of the LED array.
 7. The LED lamp of claim 6,further comprising: a seventh diode having an anode connected to thesecond end of the fourth capacitor and a cathode connected to the firstend of the LED array; and an eighth diode having an anode connected tothe second end of the LED array and a cathode connected to the secondend of the third capacitor.
 8. A light-emitting diode (LED) lampcomprising: four external connection pins; an LED array including aplurality of LEDs in series; one or more capacitors connected betweenthe LED array and the external connection pins; and one or more diodes,each of said one or more diodes being connected in parallel withcorresponding one of said one or more capacitors.
 9. The LED lamp ofclaim 8, wherein the one or more capacitors include a first capacitorhaving a first end connected to a first connection pin and a second endconnected to an anode terminal of the LED array, and a second capacitorhaving a first end connected to a second connection pin and a second endconnected to a cathode terminal of the LED array, and wherein the one ormore diodes include a first diode having an anode connected to the firstend of the first capacitor and a cathode connected to the second end ofthe first capacitor, and a second diode having a cathode connected tothe first end of the second capacitor and an anode connected to thesecond end of the second capacitor.
 10. The LED lamp of claim 9, whereinthe one or more capacitors further include at least one of: a thirdcapacitor having a first end connected to the third connection pin and asecond end connected to the anode terminal of the LED array, and afourth capacitor having a first end connected to the fourth connectionpin and a second end connected to the cathode terminal of the LED array,and wherein the one or more diodes further include at least one of: athird diode having an anode connected to the first end of the thirdcapacitor and a cathode connected to the second end of the thirdcapacitor, and a fourth diode having a cathode connected to the firstend of the fourth capacitor and an anode connected to the second end ofthe fourth capacitor.